1. Field of the Invention
The present invention relates to a terminal crimping apparatus and more particularly to a terminal crimping apparatus for crimping a terminal of an open barrel type to an end of an electric wire.
2. Description of the Related Art
As an example of a terminal to be crimped to an end of an electric wire, there is conventionally known a terminal of the opened barrel type. As shown in FIG. 1, such a terminal of the opened barrel type has a wire barrel 11 to be crimped to a conductor W1 at an end of an electric wire W, and an insulation barrel 12 to be crimped to a coated end W2 of the electric wire W. Each of the barrels 11, 12 has a substantially U-shaped section and is of linear symmetry. A terminal 1 (See FIG. 2) can be crimped to an end of the electric wire W in the following manner. With the conductor W1 and the coated end W2 of the electric wire W respectively introduced into the wire barrel 11 and the insulation barrel 12, the barrels 11, 12 are respectively caulked by two pairs of crimpers 13 and anvils 14 of a terminal crimping apparatus, each pair of crimper 13 and anvil 14 being vertically disposed with each of the barrels 11, 12 sandwiched therebetween. As a method of crimping a terminal 1, there is known a so-called overlap crimping method, as shown in FIG. 3, by which one tips 111, 121 of the barrels 11, 12 overlap the other tips 112, 122 of the barrels 11, 12 (Japanese Patent Unexamined Publication Serial No. 3-165478, Japanese Patent Unexamined Publication Serial No. 3-291881, Japanese Patent Examined Publication Serial No. 55-37840, and Japanese Utility Model Examined Publication Serial No. 52- 24784).
To carry out the overlap crimping above-mentioned, each of the crimpers 13 has a caulking surface for pushing the barrel 11 or 12, and this caulking surface has a step portion 13c, a first round portion 13a and a second round portion 13b, the first and second round portions 13a, 13b smoothly integrate with each other through the step portion 13c, as shown in FIG. 2. The step portions 13c are formed at positions biased toward the second round portions 13b with respect to the center portions 13d of the caulking surfaces. On the other hand, each of the anvils 14 has a pressure receiving surface 14a for receiving the barrel 11 or 12. The pressure receiving surfaces 14a are arcuate as depressed downwardly with respect to the drawing plane of FIG. 2 such that the barrels 11, 12 are adapted to be received.
When the crimpers 13 and the anvils 14 press the barrels 11, 12 by pinching the barrels 11, 12 therebetween, tips 111, 121 of the barrels 11, 12 move along the corresponding first round portions 13a while the other tips 112, 122 move along the corresponding second round portions 13b, utilizing the step portions 13c at the boundaries between these round portions 13a, 13b, so it is possible to caulk the tips 111, 121 of the barrels 11, 12 as overlapping the outer peripheral sides of the other tips 112, 122.
In the conventional overlap crimping mentioned above, the following is presumed. When the crimpers 13 and the anvils 14 press the barrels 11, 12 by pinching the barrels 11, 12 therebetween, the tips 111, 121 of the barrels 11, 12 are so deformed as to follow the corresponding first round portions 13a while the other tips 112, 122 are so deformed as to follow the corresponding second round portions 13b so that the tips 111, 121 ultimately overcome the step portions 13c and overlap the outer peripheral sides of the other tips 112, 122.
Dependent on the shapes of the barrels 11, 12 or the shapes of the caulking surfaces of the crimpers 13, there are instances where the tips 111, 121 of the barrels 11, 12 do not overlap the other tips 112, 122 but abut thereon, as shown in FIG. 4. This disadvantageously generates burrs B on those portions of the barrels 11, 12 which correspond to gaps between the crimpers 13 and the anvils 14. The inventor of the present application has studied what might be the cause of such defective crimping, and found the following fact.
Referring to FIGS. 5A to 5D, the following will discuss the mechanism for crimping the barrels 11, 12 by the crimpers 13 and the anvils 14. When the crimpers 13 approaches the anvils 14, the tips 111, 121 and the other tips 112, 122 of the barrels 11, 12 abut on each other in the openings of the crimpers 13. The shapes of the caulking surfaces and the opening widths at the vicinity of the openings of the crimpers 13 are determined such that the tips 111, 121 and the other tips 112, 122 are so deformed as to face each other. Accordingly, the tips 111, 121 and the other tips 112, 122 abut on each other while contacting with the first round portions 13a. As the crimpers 13 approaches further near the anvils 14 as shown in FIG. 5B, the tips 111, 121 are so deformed as to follow the first round portions 13a and the other tips 112, 122 are so deformed as to follow the second round portions 13b. As shown in FIG. 5c, the further caulking process from the state shown in FIG. 5B normally causes the other tips 112, 122 to overlap the tips 111, 121 as the other tips 112, 122 are pressed downwardly by the step portions 13c when the tips 111, 121 and the other tips 112, 122 follow respectively the corresponding round portions 13a, 13b to a certain extent, so that the other tips 111, 121, as shown in FIG. 5D, ultimately overcome the step portion 13c, thus completing the crimping processing.
In view of the foregoing, the inventor has found that the cause of defective crimping resides in the fact that the caulking step has been advanced without release of the state that the tips 111, 121 abut on the other tips 112, 122 (FIG. 5A).
Accordingly, what is really needed is a terminal crimping apparatus that can prevent the tips of a barrel from abutting on each other, thus preventing a crimped terminal from being defectively crimped.
In crimping a terminal 1, it is required that the electrical connection between the conductor W1 of the electric wire W and the wire barrel 11 is perfectly assured and that there is provided a crimping strength substantially equal to the tensile strength of the electric wire W. Therefore, the crimping quality is conventionally checked by measuring the crimp height H of the crimped terminal 1 (e.g., Japanese Patent Unexamined Publication Serial No. 2-257001).
FIG. 6 is a perspective view of a measuring device 2 for measuring the crimp height H. The measuring device 2 comprises a frame 20, a dial gauge 21 supported by the frame 20, a block-like movable contact piece 22 disposed at the tip of a measuring head of the dial gauge 21, and a block-like stationary contact piece 23 disposed opposite to and under the movable contact piece 22. As shown in FIG. 7, a measuring surface 22a of the movable contact piece 22 and a measuring surface 23a of the stationary contact piece 23 are horizontal and parallel to each other.
The crimp height H is measured in the following manner. As maintained in a posture in a crimping step, the crimped portion X of the crimped terminal 1 is held by and between the measuring surfaces 22a, 23a, and the scale on the dial gauge 21 is then read.
To measure the accurate crimp height H, it is required that the crimped portion X of each of the barrels 11, 12 is clamped between the measuring surfaces 22a, 23a while maintaining each of the barrels 11, 12 in a caulked posture.
In the conventional overlap crimping, however, a line L, which connects a contact point S1 where the measuring surface 22a of the movable contact piece 22 comes in contact with the crimped portion X to a contact point S2 where the measuring surface 23a of the stationary contact piece 23 comes in contact with the crimped portion X is inclined at a predetermined angle .theta. with respect to the clamping direction of the crimped terminal 1 by the contact pieces 22, 23, or the perpendicular direction, as shown in FIG. 7. Accordingly, when the crimped portion X is clamped between the contact pieces 22, 23, a moment of rotation is inevitably applied to the crimped terminal 1, causing the crimped terminal 1 to be rotated around the electric wire W. This may disadvantageously produce a measuring error, thus failing to make an accurate judgment of whether the crimping is good or defective.
Accordingly, what is needed is a terminal crimping apparatus capable of accurately measuring the crimp height of the crimped terminal.